Poultry vaccination is widely used to protect poultry flocks against devastating diseases including Newcastle disease (ND), infectious bursal disease (IBD), Marek's disease (MD), infectious bronchitis (IB), infectious laryngotracheitis (ILT) and avian influenza (AI). ND is caused by the avian paramyxovirus 1 (APMV-1) also designated ND virus (NDV) belonging to the Paramyxoviridae family. MD is caused by Gallid herpesvirus 2 (Herpesviridae family) also designated as MD virus serotype 1 (MDV1). IB is caused by IB virus (IBV) belonging to the Coronaviridae family, ILT is caused by Gallid herpesvirus 1 (Herpesviridae family) also designated ILT virus (ILTV) and AI is caused by AI virus (AIV) belonging to the Orthomyxoviridae family.
A number of recombinant avian viral vectors have been proposed with a view to vaccinating birds against these avian pathogens. The viral vectors used comprise avipox viruses, especially fowlpox (EP-A-0,517,292), Marek's virus, such as serotypes 2 and 3 (HVT) (WO-A-87/04463), or alternatively the ITLV, NDV and avian adenovirus. When some of these recombinant avian viral vectors were used for vaccination, they display variable levels of protection.
Several recombinant herpesvirus of turkeys (HVT, also designated Meleagrid herpesvirus 1 or MDV serotype 3) vectors expressing antigens from various pathogens (U.S. Pat. Nos. 5,980,906, 5,853,733, 6,183,753, 5,187,087) including IBDV, NDV, ILTV and AIV have been developed and licensed. Of particular interest is a HVT vector-expressing IBDV VP2 protective gene that has shown clear advantages over classical IBD vaccines (Bublot et al J. Comp. Path. 2007, Vol. 137, S81-S84; U.S. Pat. No. 5,980,906). Other HVT vectors of interest are those expressing either NDV (Morgan et al 1992, Avian dis. 36, 858-70; U.S. Pat. No. 6,866,852; U.S. Pat. No. 5,650,153) or ILTV (Johnson et al, 2010 Avian Dis 54, 1251-1259; U.S. Pat. No. 6,299,882; U.S. Pat. No. 5,853,733) protective gene(s). One of the practical problems of using several HVT-based recombinant vaccines together is their interference. Lower protection is induced at least against one of the disease when two HVT recombinants expressing different antigens are mixed (Rudolf Heine 2011; Issues of the Poultry Recombinant Viral Vector Vaccines which May Cause an Effect on the Economic Benefits of those Vaccines; paper presented at the XVII World Veterinary Poultry Association (WVPA) Congress in Cancun, Mexico, Aug. 14-18, 2011; Slacum G, Hein R. and Lynch P., 2009, The compatibility of HVT recombinants with other Marek's disease vaccines, 58th Western Poultry Disease Conference, Sacramento, Calif., USA, March 23rd-25th, p 84).
The combination of HVT and SB-1, a Gallid herpesvirus 3 (MDV serotype 2 or MDV-2) vaccine strain, has shown a synergistic effect on MD protection (Witter and Lee, 1984, Avian Pathology 13, 75-92). To address the interference problem, it is of interest to evaluate the HVT virus as a vaccine vector to express one or more protective antigen(s) against a variety of avian pathogens.
The SB-1 genome was cloned and characterized in bacterial artificial chromosome (BAC) (Petherbridge, et al., J. Virol. Methods 158, 11-17, 2009; Singh et al., Research in Veterinary Science 89, 140-145, 2010). The MDV2 SB-1 sequence was recently obtained and analyzed (Spatz and Schat, Virus Gene 42, 331-338, 2011). A glycoprotein E deletion of SB-1 virus was described by Petherbridge, et al. (J. Virol. Methods 158, 11-17, 2009). However, no research has been reported using SB-1 as a viral vector expressing foreign protective genes.
Considering the potential effect of animal pathogens, such as NDV and IBDV on veterinary public health and the economy, efficient methods of preventing infection and protecting animals are needed. There is a need for a solution of combined effective vector vaccines and a suitable method for making the vaccine that could alleviate the problem of interference observed between two HVT-based vector vaccines.